The present invention pertains to apparatus and methods for realigning any abnormal curvature of the spine and more particularly to posterior instrumentation having claw-like clamp sets to affix to vertebrae which enable reduction of the vertebrae followed by attachment to a precontoured rail to reduce spinal deformities such as scoliosis.
A normal spine when viewed from an anterior or posterior perspective is longitudinally aligned with a straight vertical line. The spine when viewed from either side presents a series of curvatures. The top curve in the neck or cervical spine has a convexity pointing anterior or towards the front. This type of curve (convexity pointing anterior) is called a lordotic curve. The next lower curve in the chest area or thoracic spine has a convexity pointing posterior or towards the back. This type of curve (convexity pointing posterior) is called a kyphotic curve. The lowest curve in the low back or lumbar area again has a convexity pointing anteriorly.
Scoliosis is a deformity of the spinal column with three components. The first is an apparent side bending of the spine when viewed from the front or back (anterior/posterior or AP view). This is a coronal plane deformity. The second component is a loss of the normal kyphotic curvature in the thoracic or chest area when viewed from the side. This is a sagittal plane deformity. The third component is the rotation of the spine around its own long axis. This is an axial plane deformity. This latter deformity can be appreciated on either a cross sectional x-ray study such as a CT scan (computerized axial tomography scan) or more importantly from the effect on the attached ribs. It is this rotation that causes the characteristic xe2x80x9crib humpxe2x80x9d which is the most disturbing element of the deformity to the patient and the aspect of the deformity that is least well treated by current surgical treatment methods. Depending on the etiology of the spinal deformity, one or more instances of abnormal curvature may be present in the scoliotic spine and depending on the gravity of the deformity, the preferred treatment may involve surgical procedures. In severe cases, bone fusion and instrumentation may be indicated. Instrumentation merely serves to hold the vertebrae in their correct alignment while the bone fusion heals. Thus, in order to be effective, instrumentation must be able to correct vertebral alignment deformities in both the coronal and sagittal planes as well as correct for rotational aberrations.
Several procedures are available which include the use of either anterior or posterior instrumentation. Anterior and posterior instrumentation have their specific uses in different cases with attendant advantages and disadvantages. Posterior instrumentation is usually recommended for a typical deformity seen in patients which is known as a right thoracic curvature. One benefit to posterior instrumentation is its relatively less invasive nature as compared with most anterior methods.
Generally, posterior instrumentation involved the use of two longitudinal rods secured to the spine by the use of multiple hooks, wires or sometimes screws and to each other with connecting plates. The standard method of spinal deformity reduction was to attach a pre-bent, pre-cut rod in the anticipated correction shape to the spine with a loose connection between the rod and hooks via several types of known connectors. The rod was then rotated inside the connectors into the improved position. The connectors were then locked connecting the hook securely to the rod. A second rod was attached to the spine in a similar way with little if any correction obtainable at that time. Two plates or cross connectors were then attached to link the two rods together into one effective unit.
This method had several disadvantages. First, this technique most effectively corrected the sagittal and coronal plane deformities but did little if anything for the axial deformity. Second, since each hook was attached to its own respective single vertebra, all corrective force was applied to the vertebra in one location increasing the chance of hook cutout through the lamina. Third, since the rod was rotated with a loose connection, there existed the possibility for the hook to dislodge from the lamina sometimes with catastrophic consequences for the patient""s spinal cord. Fourth, since a scoliotic deformity is an axial rotation of a free body (the vertebra) without a fixed pivot, it requires two simultaneous forces in opposite directions around an axis (a torque) to correct it. This concept was addressed in an earlier patent concerning a two rod system. No current system provides this. Fifth, a two rod system leaves the rods in a lateral position where the paraspinal muscles are suppose to attach to the bone to help heal the spinal fusion. Sixth, since the rod is pre-bent and pre-cut to length before the correction is obtained and the rigidity of the patient""s spine is variable and hard to measure preoperatively, the ultimate length and shape are determined from an educated guess.
In view of the short comings of the existing procedures for treating scoliotic spines, there is a need for improvements which allow the use of a single-rod system that will reduce the scoliotic spine in all three planes, distribute the force during reduction over the vertebra, will attach rigidly to the spine before the reduction maneuver, will apply a true derotation torque to correct the axial plane deformity, will leave the longitudinal rod in a more biologically advantageous central place (where the spinous process was), and allow reduction of the deformity before cutting and contouring the rod.
The present invention relates to an apparatus and method for reducing a scoliotic spine. The apparatus includes at least one vertebral clamp set having a plurality of laminar hooks and a coupling member for receiving a single central rail. The rail is cut and contoured to a corrected alignment of the spine so that it can be attached to one or more clamp sets after reduction of the spine has been performed.
A preferred embodiment of the present invention includes four clamp sets and a single rail, each clamp set has a transverse plate with a center region, and a first and second end. The first end has a pedicle extension to transmit force to a pedicle of a vertebra during reduction and the second end also has a pedicle extension to transmit force to a pedicle during reduction of the vertebra when the force is applied in the opposite direction. The plate has a first laminar hook to hook on a superior portion of a first lamina of a vertebra. The first hook is located on the first end of the plate and is integral with the plate. The plate has a second laminar hook to hook on an inferior portion of a second lamina of a vertebra, such that the first and second hook are in opposed configuration, giving a claw-like hold on the vertebra. The second hook is located on the second end of the plate and is made adjustable with the plate to facilitate clamping and unclamping. The plate also includes a rail coupling member having a slot to receive a precontoured rail. The slot surface is configured to engage the rail cross-sectional area and shape. The rail will preferably be multisided having between 16 to 24 sides, and possibly as little as 4 to as many as 120.
In another embodiment of the present invention, a clamp set for reducing spinal deformity is disclosed. The clamp set for affixing to a vertebra has a transverse plate having a center region and a first and a second end. The first end has a first pedicle extension, and the second end has a second pedicle extension. At least one pedicle extension is used to transmit a downward force during reduction of the vertebra. The clamp set also includes a first laminar hook located on the first end of the plate and is integral with the plate to hook on a superior portion of a first lamina of a vertebra. The clamp set also includes a second laminar hook to hook from an opposite direction on an inferior portion of a second lamina of the same vertebra. The second hook is adjustable to allow clamping and unclamping of the clamp set. The clamp set includes a rail coupling member having a slot to receive a rail. The rail coupling member is located on the center region of the plate, and the slot is configured to accept the rail cross-sectional area and shape.
In another embodiment of the present invention, a method for reducing the spine is disclosed. The method will include the steps of: attaching a plurality of vertebral clamp sets to vertebrae along the extent of the deformity of the spine, attaching reduction clamps to the vertebral clamps, attaching self-retaining arms to the reduction clamps in a loosened state, reducing the vertebra sequentially by grasping the reduction clamp and maneuvering it into an optimal position and the holding it there by securing the self retaining arm in a rigid condition, then once the optimum position has been obtained, cutting and contouring the rod to the reduced spine. The rail (rod) is then secured to the individual central connectors and the reduction clamps are removed.
Many advantages are obtained with the use of posterior instrumentation constructed in accordance with the present invention. One advantage of a single rail system over a double rod system is that a single rail causes less disruption of the healing muscles and allows more area for bone grafts. Another advantage is more secure instrumentation attached to the individual vertebra as compared with singular bone hooks which may shear from their lamina and cause damage to bone or nerve tissue. Another advantage is having a rail contoured to the spine after reduction has taken place which avoids incorrect rail length and over-compensation or under-compensation of the rail contours. Another advantage is the use of a clamp set with pedicle extensions which distribute rotational forces downward onto the pedicle rather than solely on the lamina during reduction of the vertebra, thus allowing greater rotational forces without fear of damaging bone tissue or popping hooks from their laminae. Another advantage is the use of a multi-sided rail which allows for fine adjustment of the degree of reduction without slippage between the clamp sets and the rail, and thus can eliminate the use of a two rod system and further provides greater rotational stability.